142 Questions
What is the purpose of the recommended practice for electrical installations in petroleum facilities?
To provide information on preventing accidental ignition of flammable liquids and gases
Why are the requirements for electrical systems in petroleum facilities more stringent?
Due to the specialized equipment and high rates of processing
What is excluded from the scope of the recommended practice for electrical installations in petroleum facilities?
Electrical equipment test standards
What is the focus of the recommended practice for electrical installations in petroleum facilities?
Designing to prevent accidental ignition of flammable liquids and gases
Which organization provides guidelines for area classification and selection of electrical equipment in petroleum facilities?
API RP 500 and RP 505
What is the primary purpose of positive-pressure ventilation in relation to classified locations?
To reduce or eliminate classified locations
Which technique is primarily used for instrumentation and process control in classified areas?
Intrinsically safe equipment and wiring methods
What can energy efficient electrical design lead to in terms of losses and costs?
1.5% fewer losses and significant cost savings
What is the potential range of electrical losses in the distribution and utilization equipment of a refinery power system?
As high as 20%
Which organization must approve electrical equipment for specific area classification?
Nationally Recognized Testing Laboratory (NRTL)
What are the alternative designs for installing equipment not suitable for classification?
Physical isolation, pressurized rooms, and intrinsically safe installations
Which protection technique is NOT mentioned for electrical equipment in classified areas?
Increased ventilation
What is the primary purpose of intrinsically safe equipment and wiring methods?
For instrumentation and process control
What is the focus of economic evaluation, power factor, and demand control in relation to electrical efficiency?
Energy efficiency
What can reduced losses in electrical equipment result in?
Lower operating temperatures and prolonged equipment life
Which document provides guidelines for electrical equipment for specific area classification?
NFPA 70
Which classification system is used for locations containing flammable gases or vapors?
Division system
What are the classes into which flammable liquids are divided based on flash and boiling points?
IA, IB, and IC
Which organization provides detailed guidelines for the classification of locations containing flammable liquids and gases?
API
What are the criteria established by NFPA 70 for classifying locations?
Flammable gases, vapors, combustible dust, ignitable fibers or flyings
What determines the physical boundaries of a classified location?
Quantity and physical characteristics of the substance, its tendency to disperse, and the need for air to become ignitable
What serves as a reference for selecting and locating electrical equipment in classified locations?
Plot plan
What are the categories used in the Zone system for classifying locations containing flammable gases or vapors?
Zone 0, Zone 1, and Zone 2
What is the purpose of a plot plan in the context of location classification?
To serve as a reference for selecting and locating electrical equipment
Which organization's classifications are applied to electrical installations in petroleum facilities by API RP 500 and 505?
NFPA 70
What are the categories used in the Division system for classifying locations containing flammable gases or vapors?
Division 1 and Division 2
What is the term for locations not classified as Division 1, Division 2, Zone O, Zone 1, or Zone 2?
Unclassified locations
What is efficiency defined as?
The ratio of power output to power input
How much raw fuel is saved by a 1 kWh reduction in electrical usage?
4 to 5 kWh
What can be used to calculate the dollar-per-kilowatt factor?
Simple payback
How much can cogeneration increase the generation cycle thermal efficiency by when waste heat is recovered?
From about 25% to about 70%
What is recommended for determining equipment efficiency if economic penalty factors are involved?
Witnessed testing
What should be clearly stated in the equipment specification if payment terms are contingent on receipt of test results?
Payment terms
What should the economic evaluation account for, especially for very large projects?
Depreciation, tax investment credits, and variable escalation rates
How can power costs be reduced?
Investing in in-plant generation, particularly through cogeneration
What should specifications for electrical equipment include consideration for?
Energy efficiency, including operating points and efficiency curves
What does reduced losses in indoor applications do to the heat load on air conditioning equipment?
Decrease the heat load
What does energy efficient electrical equipment normally demand?
A premium price
What is necessary to determine if the equipment costs will be offset by future energy savings?
Economic evaluation
What is the typical efficiency of typical utility generating units?
35%
What is the temperature range for the exhaust gases used in the waste heat boiler?
500°C to 600°C
What are three examples of direct heating with turbine exhaust?
Heating viscous products, heating process feeds, supplying thermal energy for absorption refrigeration cycles
What is used to heat the product when gas turbines are used as generator drives to provide power for the transport pump motors?
Exhaust exchanger
What is displaced by using the waste heat from the gas turbine’s exhaust in process plants?
Fuel
What is the purpose of the power recovery turbine?
To recover energy from the regenerator flue gases
What is the typical output range of the generator used in the power recovery turbine system?
5 MW to 10 MW
What type of generator is usually used for the power recovery turbine service?
Induction generator
What is used as a source of electric power by dropping the line pressure to plant utility pressure through an expander?
Fuel gas
What is the efficiency of high-efficiency transformers that can be purchased?
99%
What are the two components of transformer losses?
No-load losses and load losses
Which losses are considered to be constant for a given voltage?
Core losses
What are the most significant losses caused by the flow of load current in both primary and secondary windings of transformers?
12R losses
What is the major consumer of energy in process plants, typically accounting for 70% of the electrical energy consumption?
Motor loads
What are the motor losses consisting of, apart from core loss and stray-load loss?
Friction and windage
What is the purpose of suitable relaying in parallel operation of incoming utility lines?
To protect the system from overload and faults
What should be considered when incoming circuits cannot be paralleled?
Implementing automatic transfer between the circuits
What should be included in a regular testing method for the automatic transfer scheme?
Synchronization check relays
What should be considered for maintaining close voltage regulation when utility or plant voltage varies?
Automatic load-tap-changing transformers
What can harmonic distortion cause in electrical systems?
Overloading and overheating
What must the electrical system be designed to accommodate in terms of short-circuit current?
Maximum short-circuit current
What is essential to minimize the number and duration of power outages?
Proper relaying
What should be calculated to ensure that plant and utility company requirements are met during motor starting?
Voltage drop
What is typically used to parallel incoming utility lines on the substation bus?
Relay protection systems
What should be reviewed for systems with appreciable nonsinusoidal harmonics?
IEEE Std 399 and Std 519
What should be known to determine the effect on motor starting and protective relay settings?
Short-circuit current level
What is essential to consider for maintaining system protection and reliability?
Suitable relaying
What type of auxiliaries are critical for air, fuel, and water supplies in power stations producing steam and electricity?
Critical auxiliaries
What type of construction can be used in isolated power stations where each generator has its own boiler or turbine, main bus, and auxiliary bus?
Unit construction
What serves to limit fault duty and isolate voltage dips during faults in a synchronizing bus scheme?
Reactors
What is crucial for the reliable generation of reactive power by the generator field?
Excitation system
What are the two types of excitation systems commonly used for generators?
Brushless and static exciters
What should be examined to determine the frequency and nature of service disturbances, automatic reclosures, and outage lengths?
Performance records of utility feeders
What should circuits be sized for in order to ensure continuous load carrying capacity?
Peak demand
What should be provided by utilities to assess the reliability of the utility system?
Performance records of pertinent utility feeders
What should power contracts with utilities include consideration for?
All of the above
What should be examined to determine the capacity to carry the load continuously if any one circuit is out of service?
Circuit protection details
What should energy charges in power contracts with utilities include as part of the contract?
Fuel adjustment costs
What should be examined to determine the reliability of the utility system?
Performance records of pertinent utility feeders
What is the formula for calculating power factor?
Power factor = kW / kVA
What is the unit of expression for apparent power consumed by an electrical system?
Kilovolt-amperes (kVA)
What is the primary purpose of power factor correction capacitors in a system?
To supply the reactive requirements of inductive loads
What is the equivalence of British thermal units (Btu) to other units?
1 Btu = 1055 Joules
What determines the energy loss in power cables?
The amount of current expected to flow in the circuit
What is the relationship between kilowatts (kW) and kilovolt-amperes reactive (kvar) in an electrical system?
kW and kvar are components of apparent power (kVA)
What action can be taken to reduce higher-than-necessary currents on the distribution system due to low power factor?
Using high power factor rated equipment
What is the primary benefit of installing capacitors at the motor terminals and switching them on and off with the motor?
Reducing power factor
What is the relationship between raw fuel consumption and electricity production in a conventional utility generating station?
Approximately 10,000 Btu of raw fuel produces 1 kWh of electricity
What is the measure of the percentage of kVA that is doing useful work in an electrical system?
Power factor
What is the primary effect of low power factor in a system?
Higher-than-necessary currents on the distribution system
What is the primary factor that determines the energy loss in power cables?
The resistance of the cable
What is a factor to be considered for the design of protective relaying and system control schemes?
Voltage level of the feeder
What should be taken into consideration for the characteristics of a facility substation?
Grounding
What may be required when the utility system is not stiff enough to allow full-voltage starting of the largest motor?
Reduced-voltage starting
What is a consideration for maintaining close voltage regulation when utility or plant voltage varies?
Spare transformer capacity
What impacts all factors and is crucial in power system design?
Maintainability of equipment
What is the purpose of dual-purpose fault clearing devices?
To provide both sensing and interrupting functions in the same enclosure
Which system is the easiest to understand, operate, and troubleshoot but provides no alternate power source?
Simple radial system
What is the primary function of single-purpose fault clearing devices?
To receive electrical signal from relay to interrupt electric current
Which system offers uninterrupted service continuity and voltage regulation to all loads, but is complex and costly?
Secondary-selective parallel system
What is the purpose of establishing a zone of protection around each system element?
To properly isolate faulted section
What do power system planning, design, and operation require continual and comprehensive analyses to evaluate?
Stability
What is the importance of obtaining optimum settings for fault clearing device coordination?
To ensure coordinated fault clearing devices properly isolate faulted section
What must fault-current interruption devices have to handle available fault currents and prevent equipment failure?
High interrupting rating
What is the primary function of a relay in the electrical system?
To detect abnormal system conditions and initiate breaker operation
What can faults not promptly isolated from the power source cause?
Fires and production interruptions
What is the purpose of proper selection and application of relays?
For protection of feeders, transformers, and rotating machines
What is crucial in system design and impacts all factors?
Maintainability of equipment
What can relays be adjusted for?
Selectivity and proper operation ranges
Which system offers better service continuity and flexibility than a simple radial system, but with higher initial investment?
Primary-selective radial system
What is required for relays to ensure proper settings and operation?
Testing and inspection
What do system studies include to evaluate current system performance and the effectiveness of alternative plans for expansion?
Reliability
What initiates the operation of a breaker in the electrical system?
Relay detecting abnormal system conditions
What is the most correct about a simple radial system?
Provides no alternate power source
What is the focus of IEEE Std 242 and WEE Std 141?
Coordination margins for fault clearing devices
What is required to handle available fault currents and prevent equipment failure?
High interrupting rating
What is the primary function of fault sensing devices in the electrical system?
To detect fault in electrical system
What is the primary purpose of fault considerations in system design?
To ensure safety
What must fault clearing devices have to ensure proper operation during faults?
Adequate interrupting and momentary withstand ratings
What is the primary purpose of power factor correction capacitors in a system?
To improve the power factor of the system
What serves to limit fault duty and isolate voltage dips during faults in a synchronizing bus scheme?
Protective relaying
What are the categories used in the Zone system for classifying locations containing flammable gases or vapors?
Zone 0, Zone 1, Zone 2
What is the purpose of the power recovery turbine?
To generate electrical power from waste heat
What is essential to consider for maintaining system protection and reliability?
Equipment fault duty ratings
What are the two components of transformer losses?
Core loss and stray-load loss
What is the unit of expression for apparent power consumed by an electrical system?
Volt-amperes (VA)
What is the relationship between raw fuel consumption and electricity production in a conventional utility generating station?
Directly proportional
What is the purpose of the recommended practice for electrical installations in petroleum facilities?
To provide guidelines for safe and efficient electrical systems
What should specifications for electrical equipment include consideration for?
Safety and reliability
What is necessary to determine if the equipment costs will be offset by future energy savings?
Life cycle cost analysis
What is the purpose of a plot plan in the context of location classification?
To determine equipment layout
What should be considered when applying fuses to facility power systems?
Single-phasing possibilities
What is a characteristic of fuses designed for special applications such as motor starter circuits?
Current limiting
What must be considered when coordinating fuses for the power system?
Time-current characteristic envelope curve
Where are circuit breakers not listed for direct use according to NRTL?
Classified locations
What is a characteristic of circuit breakers used on systems with nominal system voltages of 600 V-15,000 V?
Installed in switchgear lineups
What is the interrupting medium generally used for circuit breakers on systems with nominal system voltages of 15,000 V-35,000 V?
Air or vacuum
Where are circuit breakers installed when the utility system is not stiff enough to allow full-voltage starting of the largest motor?
Switchgear
What is the primary purpose of a regular preventive maintenance program for circuit breakers?
Establish maintenance and testing requirements and intervals
What is the primary purpose of switchgear applications?
Protect electrical system components
What is the interrupting medium generally used for higher voltage systems in individual free-standing outdoor types of circuit breakers?
Oil or SF6
What is essential for circuit breakers used on systems with nominal system voltages less than or equal to 600 V?
Variety of styles
What is the primary purpose of using relays for sensing fault conditions in circuit breakers?
Sensing abnormal conditions
Study Notes
Electrical Efficiency and Economic Evaluation of Energy Efficient Equipment
- Reduced losses in indoor applications decrease the heat load on air conditioning equipment.
- A 1 kWh reduction in electrical usage saves the equivalent of 4 to 5 kWh of raw fuel due to losses in electricity generation, transmission, and distribution.
- Efficiency is defined as the ratio of power output to power input or energy output to energy input.
- Specifications for electrical equipment should include consideration for energy efficiency, including operating points and efficiency curves.
- Economic evaluation is necessary to determine if the equipment costs will be offset by future energy savings.
- Energy efficient electrical equipment normally demands a premium price, and a dollar-per-kilowatt factor can determine the value of saved energy for specific projects.
- The dollar-per-kilowatt factor can be calculated using simple payback, taking into account factors such as income tax rate, effective interest rate, and power cost escalation rate.
- Power costs can be reduced by investing in in-plant generation, particularly through cogeneration, which uses waste heat for process heating or power generation.
- Cogeneration can increase the generation cycle thermal efficiency from about 25% to about 70% when waste heat is recovered.
- Witnessed testing is recommended for determining equipment efficiency if economic penalty factors are involved.
- Payment terms contingent on receipt of test results should be clearly stated in the equipment specification.
- The economic evaluation should account for factors such as depreciation, tax investment credits, and variable escalation rates, especially for very large projects.
Design Considerations for Petroleum Facility Power Systems
- The text discusses the importance of evaluating design considerations for developing reliable and cost-effective power systems for continuously run petroleum facilities.
- It covers all aspects of facility power systems, including incoming lines for purchased power, in-plant generation, substations, transformers, switchgear, overhead distribution systems, voltage levels, system arrangements, protective relaying, fault currents, and system stability.
- Facility power stations not connected to public utility systems must be designed with redundancy to ensure self-sufficiency for various operating contingencies.
- Power cables' energy loss depends on the resistance of the cable and the amount of current expected to flow in the circuit.
- Apparent power consumed by an electrical system is expressed in kilovolt-amperes (kVA) and consists of a kilowatt (kW) component and a kilovolt-ampere reactive (kvar) component.
- Power factor is the ratio of kW to kVA and provides a measure of the percentage of kVA that is doing useful work.
- Low power factor in a system can result in higher-than-necessary currents on the distribution system, leading to higher losses.
- Actions to increase power factor and reduce associated losses include using high power factor rated equipment, operating high efficiency induction motors at close to design horsepower, and using power factor correction capacitors to supply the reactive requirements of inductive loads.
- When capacitors are applied to induction motors, the greatest benefit is obtained if the capacitors are installed at the motor terminals and switched on and off with the motor.
- The text provides definitions and conversion factors useful in energy discussions, such as the equivalence of British thermal units (Btu) to other units, the definition of a quad, and the conversion of horsepower to kilowatts.
- Due to thermal losses, approximately 10,000 Btu of raw fuel are consumed to produce 1 kWh of electricity in a conventional utility generating station.
- The text emphasizes the need for equipment evaluation at critical speeds and evaluating the effects of system harmonics generated by adjustable frequency drive equipment.
Electrical Fault Clearing Devices and Relaying Considerations
- Fault sensing device detects fault in electrical system
- Signal sent to fault clearing devices to isolate faulted segment
- Fault clearing devices must have adequate interrupting and momentary withstand ratings
- Dual-purpose devices provide sensing and interrupting functions in same enclosure (e.g., fuses, circuit breakers)
- Single-purpose devices receive electrical signal from relay to operate mechanical contacts to interrupt electric current
- Zone of protection established around each system element (e.g., bus, transmission line)
- Coordinated fault clearing devices must properly isolate faulted section
- Coordination margins outlined in standards such as WEE Std 141 and IEEE Std 242
- Importance of obtaining optimum settings for fault clearing device coordination
- Relay detects abnormal system conditions and initiates breaker operation
- Proper selection and application of relays important for protection of feeders, transformers, and rotating machines
- Relays can be adjusted for selectivity and proper operation ranges, and require testing and inspection for proper settings and operation
Electrical Distribution and Utilization System Design Considerations
- Electrical distribution and utilization system must be designed for regular inspection and maintenance to ensure reliable operation.
- Maintenance of electrical facilities for a petroleum facility is often done at the same intervals as other process equipment.
- Avoid connecting unrelated process equipment that cannot be shut down during the primary facility shutdown.
- Design of electrical systems should consider potential facility additions or modifications, including equipment fault duty ratings and provisions for future expansion.
- When a utility supplies part of the facility power and operates in parallel with plant generated power, considerations include division and interchange of real and reactive power, protective relaying, and service restoration procedures.
- Power interchanges between utility and industrial systems can vary due to excess plant power generation, utility power restrictions, or load adjustments to maintain constant demand on the utility system.
- Contracts for the purchase of utility power should include the amount of kilowatts and kilovars and their division or interchange between the utility and the facility.
- Protective relaying must be provided to protect the plant and its generation from faults or power loss in the utility system.
- Service restoration procedures are necessary in various fault or switching conditions that may cause facility and utility generating systems to separate.
- The selection of system voltages in a facility is primarily based on economics, with consideration given to factors such as total connected load, planning for future growth, and plant standardization of equipment.
- The voltage levels in a facility are categorized as low (≤600 V), medium (601 V to 69,000 V), and high (>69,000 V), each serving different purposes.
- Four basic types of power system arrangements are available: radial, primary-selective radial, secondary-selective radial, and secondary-selective parallel.
Test your knowledge on electrical efficiency and economic evaluation of energy efficient equipment with this quiz. Explore concepts such as power output, energy input, operating points, efficiency curves, economic evaluation, dollar-per-kilowatt factor, cogeneration, witnessed testing, and payment terms. Understand the significance of reducing power costs and incorporating energy efficient equipment specifications.
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